Many check valves, especially for pipeline service, are manufactured with a rotatable disc for sealing which is supported within a valve chamber by means of an eccentric shaft arrangement. Both opening and closing movements require simple pivoting of the eccentrically supported disc about the support pin which is also referred to as a hinge pin. Since the valve disc must pivot into sealing contact with the seat of the valve, orientation of the hinge pin relative to the valve seat is critical and formation of sealing surfaces on the valve disc and seat is also critical. Although the valve design is of fairly simple nature, manufacture of the valve can be quite expensive since many critical surfaces within the valve must be generated relative to other critical surfaces. For example, the hinge pin support bores must be positioned in offset relation from both the center line of the flow passage and the plane of the valve seat. Expensive valve alignment problems may exist, which is of course detrimental to the commercial feasibility of the product.
In many cases, pivoting disc type check valves require the provision of a split body construction which requires complex machining and also require the provision of an efficient seal between the body sections. It is desirable to provide a check valve mechanism wherein a unitary body structure is provided to thus minimize manufacturing costs and reduce the possibility of seal failure while in service.
Many pivoting disc type check valves employ hinge pin disc supporting members having the ends thereof exposed externally of the valve. In some cases, the hinge pins must be sealed with respect to the valve body and leakage of such seals is a common misfunction, requiring the flow system to be shut down for valve replacement or repair. In other cases, closer plugs are threaded into the valve body to close and seal pivot pin openings. Where the plugs also function as bushings, plug positioning is critical and expensive.
Most pivotal disc type check valves are of relatively low pressure design and cannot be readily adapted for low pressure or high pressure service. It is desirable to provide a check valve mechanism incorporating a basic functional design which is readily adaptable to both high pressure and low pressure conditions, and is further adaptable through selective use of a variety of trim materials for various types of corrosive and erosive surface.